#!@PYTHON@
# This file is part of GNUnet
# (C) 2013, 2018 Christian Grothoff (and other contributing authors)
#
# GNUnet is free software: you can redistribute it and/or modify it
# under the terms of the GNU Affero General Public License as published
# by the Free Software Foundation, either version 3 of the License,
# or (at your option) any later version.
#
# GNUnet is distributed in the hope that it will be useful, but
# WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
# Affero General Public License for more details.
#
# You should have received a copy of the GNU Affero General Public License
# along with this program.  If not, see <http://www.gnu.org/licenses/>.

from __future__ import absolute_import
from __future__ import print_function
import argparse
import random
from math import ceil, log, floor
from past.builtins import xrange


def bsc(n):
    """ count the bits set in n"""
    l = n.bit_length()
    c = 0
    x = 1
    for _ in range(0, l):
        if n & x:
            c = c + 1
        x = x << 1
    return c


def simulate(k, n, verbose):
    assert k < n
    largest_arc = int(2**ceil(log(n, 2))) / 2
    num_ghosts = (2 * largest_arc) - n
    if verbose:
        print("we have", num_ghosts, "ghost peers")
        # n.b. all peers with idx<k are evil
    peers = range(n)
    # py2-3 compatible, backwards.
    # refer to http://python-future.org/compatible_idioms.html#xrange
    info = [1 << x for x in xrange(n)]

    def done_p():
        for x in xrange(k, n):
            if bsc(info[x]) < n-k:
                return False
        return True
    rounds = 0
    while not done_p():
        if verbose:
            print("-- round --")
        arc = 1
        while arc <= largest_arc:
            if verbose:
                print("-- subround --")
            new_info = [x for x in info]
            for peer_physical in xrange(n):
                peer_logical = peers[peer_physical]
                peer_type = None
                partner_logical = (peer_logical + arc) % n
                partner_physical = peers.index(partner_logical)
                if peer_physical < k or partner_physical < k:
                    if verbose:
                        print("bad peer in connection", peer_physical, "--", partner_physical)
                    continue
                if peer_logical & arc == 0:
                    # we are outgoing
                    if verbose:
                        print(peer_physical, "connects to", partner_physical)
                    peer_type = "outgoing"
                    if peer_logical < num_ghosts:
                        # we have a ghost, check if the peer who connects
                        # to our ghost is actually outgoing
                        ghost_partner_logical = (peer_logical - arc) % n
                        if ghost_partner_logical & arc == 0:
                            peer_type = peer_type + ", ghost incoming"
                    new_info[peer_physical] = new_info[peer_physical] | info[peer_physical] | info[partner_physical]
                    new_info[partner_physical] = new_info[partner_physical] | info[peer_physical] | info[partner_physical]
                else:
                    peer_type = "incoming"
                if verbose > 1:
                    print("type of", str(peer_physical) + ":", peer_type)
            info = new_info
            arc = arc << 1
        rounds = rounds + 1
        random.shuffle(peers)
    return rounds


if __name__ == "__main__":
    parser = argparse.ArgumentParser()
    parser.add_argument("k", metavar="k", type=int, help="#(bad peers)")
    parser.add_argument("n", metavar="n", type=int, help="#(all peers)")
    parser.add_argument("r", metavar="r", type=int, help="#(rounds)")
    parser.add_argument('--verbose', '-v', action='count')

    args = parser.parse_args()
    sum = 0.0
    for n in xrange(0, args.r):
        sum += simulate(args.k, args.n, args.verbose)
    print(sum / args.r)
